2 November 2016 - Case of the Week #406

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Case of the Week #406

Clinical history:
A 60 year old woman presented with an incidental finding of a 18 x 11 mm hypoechoic mass with well defined borders in the tail of the pancreas. Fine needle aspiration was performed.


Micro images:

10x

40x

H&E




What is your diagnosis?































Diagnosis:
Pancreatic splenule


Discussion:

Special stains:

CD8

CD56

Chromogranin

Synaptophysin



Test question (answer at end):

Which of these statements about an accessory spleen is true?

A. An accessory spleen is found in <5% of autopsy cases.
B. An accessory spleen has distinctive imaging features by ultrasound.
C. An accessory spleen has distinctive histology.
D. An accessory spleen may mimic a pancreatic endocrine neoplasm.

An accessory spleen is found in up to 20-30% of autopsy cases (N Engl J Med 1981;304:1111). Approximately 17% are located near the pancreatic tail (Pancreas 2011;40:956). On endoscopic ultrasound (EUS), intrapancreatic spleens may have either hypoechoic or hyperechoic features (Gastrointest Endosc 2000;52:769).

On CT, the patient was noted to have a normal spleen in addition to an enhancing nodule found in the tail of the pancreas. The nodule was an incidental finding on abdominal CT following a motor vehicle accident. Of note, ectopic spleens typically mimic neuroendocrine tumors on imaging due to high vascularity (Cibas: Cytology: Diagnostic Principles and Clinical Correlates, 4th ed, 2014).

On aspiration, the red pulp of the spleen is often seen as a mix of small lymphocytes, plasma cells and sinus histiocytes, while the white pulp consists of variably sized lymphocytes and thin walled vessels. In one case report, poorly formed pseudorosette-like structures were seen, thought to possibly represent endothelial cells (Diagn Cytopathol 2013;41:466). The differential diagnosis may include pancreatic endocrine neoplasm or solid pseudopapillary tumor. Immunohistochemical stains may be helpful in distinguishing these entities and avoiding resection of this benign lesion. As in this case, CD8 characteristically highlights the endothelium of thin walled vessels in ectopic splenic tissue (Cibas: Cytology: Diagnostic Principles and Clinical Correlates, 4th ed, 2014).


Answer to test question: D

A. An accessory spleen is found in <5% of autopsy cases - false - it is found in 20-30% of autopsy cases.
B. An accessory spleen has distinctive imaging features by ultrasound - false - it may be hypo- or hyperechoic.
C. An accessory spleen has distinctive histology - false - it is nonspecific, and may resemble normal spleen.
D. An accessory spleen may mimic a pancreatic endocrine neoplasm - true - IHC may be useful to differentiate.

Discussion edited by: Dr. Hillary Z. Kimbrell, Myriad Genetics, Inc., Utah (USA)